Symptoms of abnormal heart rhythms are generally referred to as cardiac arrhythmias, with an abnormally rapid rhythm being referred to as tachycardia. The present invention is concerned with the treatment of tachycardias which are frequently caused by the presence of an "arrhythmogenic site" or "accessory atrioventricular pathway" close to the inner surface of the chambers of a heart or in the pulmonary veins. The heart includes a number of normal pathways which are responsible for the propagation of electrical signals from the upper to the lower chambers necessary for performing normal systole and diastole function. The presence of arrhythmogenic site or accessory pathway can bypass or short circuit the normal pathway, potentially resulting in very rapid heart contractions, referred to here as tachycardias.
Treatment of tachycardias may be accomplished by a variety of approaches, including drugs, surgery, implantable pacemakers/defibrillators, and catheter ablation. While drugs may be the treatment of choice for many patients, they only mask the symptoms and do not cure the underlying causes. Implantable devices only correct the arrhythmia after it occurs. Surgical and catheter-based treatments, in contrast, will actually cure the problem, usually by ablating the abnormal arrhythmogenic tissue or accessory pathway responsible for the tachycardia. It is important for a physician to accurately steer the catheter to the exact site for ablation. Once at the site, it is important for a physician to view the surrounding environment through the x-ray having contrast media enhancement and control the emission of energy to ablate the tissue within the heart or in the pulmonary veins.
Of particular interest to the present invention are radiofrequency (RF) ablation techniques that have been proven to be highly effective in tachycardia treatment while exposing a patient to minimal side effects and risks. RF catheter ablation is generally performed after conducting an initial mapping study where the locations of the arrhythmogenic site and/or accessory pathway are determined by the assistance of x-ray having contrast media. After a mapping study, an ablation catheter is usually introduced to the target heart chamber and is manipulated so that the ablation tip electrode lies exactly at the target tissue site. RF energy or other suitable energy is then applied through the tip electrode to the cardiac tissue in order to ablate the tissue of arrhythmogenic site, the accessory pathway, or the focal atrial fibrillation. By successfully destroying that tissue, the abnormal signal patterns responsible for the tachycardia may be eliminated. Atrial fibrillation is believed to be the result of the simultaneous occurrence of multiple wavelets of functional re-entry of electrical impulses within the atria, resulting in a condition in which the transmission of electrical activity becomes so disorganized that the atria contracts irregularly. Once considered a benign disorder, AFib now is widely recognized as the cause of significant morbidity and mortality. The most dangerous outcome from AFib is thromboembolism and stroke risk, the latter due to the chaotic contractions of the atria causing blood to pool. This in turn can lead to clot formation and the potential for an embolic stroke. According to data from the American Heart Association, about 75,000 strokes per year are AFib-related.
A catheter utilized in the endocardial RF ablation is inserted into a major vein or artery, usually in the neck or groin area. For focal AFib indications, a catheter is approached from the atrium to the ostium of a pulmonary vein. The tip section of a catheter is referred to hereby as the portion of that catheter shaft containing the electrode means that may be deflectable. The electrode means is to be positioned against the ostium of the pulmonary vein or preferably inside the vein, whereby the electrode means having a firm wire, a ring electrode, an orthogonal electrode, a cap electrode, a guidewire, a mesh, or coil electrode means for lesion ablation.
The impedance usually rises at the tissue contact site when RF energy is delivered through an electrode. To create a deeper and larger controlled lesion, the surface of the tissue contact sites is preferred to maintain a proper temperature by fluid irrigation means to partially compensate for the temperature rise due to RF energy delivery.
The tip section of a catheter is referred to hereby as the portion of that catheter shaft containing at least one electrode. In one embodiment, a catheter utilized in the endocardial RF ablation is inserted into a major vein or artery, usually in the neck or groin area. The catheter is then guided into an appropriate chamber of the heart by appropriate manipulation through the vein or artery. The tip of a catheter must be manipulatable by a physician from the proximal end of the catheter, so that the electrodes at the tip section can be positioned against the tissue site to be ablated. The catheter must have a great deal of flexibility in order to follow the pathway of major blood vessels into the heart. It must permit user manipulation of the tip even when the catheter body is in a curved and/or twisted configuration. The tip section of a conventional electrophysiology catheter that is deflectable usually contains one large electrode about 4 to 8 mm in length for ablation purpose. The lesion is generally not deep because of potential impedance rise of tissue in contact with the catheter electrode and the ablation time needs to be cut short.
Accisano III in U.S. Pat. No. 5,571,085 discloses a steerable open lumen catheter, wherein the contrast media flow through a luminal conduit and vent out at an opening indiscriminately. Since contrast medium has generally a viscosity around 4 centipoises at body temperature, as compared to that for water at 0.7 centipoises, an open lumen catheter without specific flow direction would make x-ray visualization via contrast media almost worthless because of big difference in viscosity and substantial dilution of contrast media by the flowing blood. Contrast medium is hypertonic under conditions of use and may cause severe adverse events. Only adequate minimal amount should be injected for x-ray enhancement. Accisano III does not teach the usage of a minimal amount of contrast media with a directional focal injection for local x-ray enhanced visualization.
Contrast medium is also known as a diagnostic radiopaque medium. One example is iothalamate meglumine injection U.S.P., having a trade name Conray.RTM. that is manufactured by Mallinckrodt Medical. Angiography may be performed following intravascular injection that will permit general visualization until significant hemodilution occurs. To optimize contrast visualization effect, directional contrast enhancement or focal contrast enhancement at a local tissue site is extremely important in the atrial fibrillation ablation in a pulmonary vein approach. Since it is a viscous fluid, the contrast medium is preferred to be injected locally at a desired tissue site before any significant hemodilution occurs.
Therefore there is a clinical need for a new and improved catheter probe for localizing the contrast media irrigation means inside a blood vessel or an open conduit by a fluid venting opening at a substantial angle from an axial reference line and by pointing the venting opening against the local tissue site.